Koi carp are a very invasive and ecosystem destructive species so when a report was received of a sighting in the stream on the western side of Hukanui Road it was a concern that potentially, there was another invasive species that we had to contend with. Fortunately, this was found not to be the case after discussing the matter with Bruno David: SCIENTIST- water, science, and strategy, at Waikato Regional Council.
He said that while the odd koi carp may appear and may even move up into the wider system, the broader catchment is not an ideal habitat for koi to do well in (other than maybe the very lower reaches near the confluence with the Waikato River mainstem). Koi carp much prefer slower flowing, warmer water to cruise around and fossick among soft substrate (mud) etc. Koi carp only become a problem (and create measurable water quality changes) in systems when they get into densities that are >80-100kg/ha and he would be extremely surprised if this ever occurred up the Mangaiti. The odd fish, therefore, would be very benign.
Carp have been around in the lower Waikato system since the late 60’s and they are very dispersive so in most cases they have already infiltrated the places that they can reliably get to and want to get to. The fact that we do not see them routinely in the Mangaiti, indicates that they do not really want to go up there as they have much better options elsewhere.
So, all round it sounds as if we are safe from this pest species. On saying that if you do see one feel free to remove it from the stream notwithstanding the “Fishing Prohibited” signs around.
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